Treatment of infertility by assisted reproduction technologies (ART) such as in vitro fertilisation (IVF) or IVF in conjunction with intracytoplasmic sperm injection (IVF/ICSI) and embryo transfer (ET) requires controlled ovarian hyperstimulation (COH) to increase the number of female gametes1. Standard regimens2 for COH include a down-regulation phase in which endogenous luteinising hormone (LH) is suppressed by administration of a gonadotropin releasing hormone (GnRH) agonist followed by a stimulation phase in which follicular development (folliculogenesis) is induced by daily administration of follicle stimulating hormone (FSH), usually at about 150 IU/day. Other molecules having FSH activity may also be used. Alternatively stimulation is started after spontaneous or induced menstruation while preventing the occurrence of an LH surge by administration of a GnRH-antagonist, usually starting on about day 6 or 7 of FSH administration. In superovulation protocols for ART, multiple follicular development is the desired aim. When there are at least 3 follicles>16 mm (one of 18 mm), a single bolus of hCG (5-10,000 IU) is given to trigger ovulation. Oocyte recovery is timed for 36-38 hours after the hCG injection.
The rationale for the use of GnRH agonists and antagonists in this context is the prevention of an untimely LH surge that would cause premature ovulation and follicle luteinisation3. GnRH agonist regimens have become the accepted norm in the clinic. It has been found that long regimens (i.e., those started in the midluteal phase of the cycle preceding ovulation induction, or before) are associated with easier patient scheduling, greater follicle yield, and overall better clinical results.4 The use of GnRH antagonists is relatively new to the clinic, but is expected to show similar benefits, with the added advantage of a shorter treatment regimen.
The prolonged administration of GnRH agonists or the administration of GnRH antagonists results in profound suppression of endogenous LH. This situation, while not incompatible with follicle development, does not mimic the natural cycle. In the natural cycle, LH levels show a gradual increase several days before the peak at midcycle.
Several groups have explored the role of chorionic gonadotropin (CG) in ovulation induction and ART. As is well known and recognised in the art, techniques or methods of ovulation induction (OI) are distinct from methods of COH, although both may involve the administration of FSH.
Filicori et al. have investigated the role of low doses of hCG, as a surrogate for LH, in controlled ovarian hyperstimulation5. hCG administration (50 IU hCG/day) was started synchronously with FSH administration and was continued on a daily basis until ovulation was triggered with a bolus of hCG. The numbers of small (<10 mm), medium (10-14 mm) and large (>14 mm) follicles were comparable between a group receiving hCG and a control group receiving FSH alone, however, the cumulative dose of FSH and the duration of FSH stimulation were reduced in the hCG treated group.
Messinis et al. report ovulation induction in anovulatory women (WHO group I) using a regimen that uses daily doses of hMG (75 IU each of FSH and LH) during the stimulatory phase and single or multiple doses of hCG during the luteal phase. The pregnancy rate was found to be significantly increased in patients receiving multiple hCG doses during the luteal phase as compared to a control group that received only a single ovulation inducing/triggering dose of hCG6.
Proper follicular development is of course essential for successful ART methods. However, there are some cases in which ovulation and fertilisation are achieved, and yet improper implantation of the embryo prevents pregnancy. In other cases, spontaneous abortion (miscarriage) occurs during the first trimester. Both these problems may be associated with conditions in the endometrium, which is quite sensitive to hormone levels.
Thus, it can be seen that even once follicular development, ovulation and fertilisation have occurred there is no guarantee of a successful pregnancy and problems with implantation and early miscarriage are often encountered.
In some patients, tendency to abort or failure to implant may eventually be overcome, but to do so requires repeated ART cycles, with consequent negative physiological and psychological effects on the patient. In other patients, these problems represent an essentially permanent stumbling block to pregnancy.
Methods for increasing implantation rates and decreasing early miscarriage rates, particularly in conjunction with COH, are thus highly desirable.